The invention relates to a process for centrifugal casting copper, copper alloys, or other alloys, wherein, in order to reduce or, respectively, avoid the oxide layer that forms on the inner surface of the casting at least one additive is introduced into the mold. In addition, the present invention relates to an apparatus for centrifugal casting copper or copper alloys with a rotatable mold a pouring tube and a delivery means for additives, that, in addition to the pouring tube, leads or can be led into the mold, particularly into the interior of the casting.
The use of borax as a flux is generally known. Further, the addition of borax is known from the US-PS 2,265,740 for centrifugal casting of iron to tubes of cast iron; in this case borax is blown onto the inner surface of the molded tubes. The DE-OS 2,422,339 describes the addition of fluxes, for example common salt, cryolite, fluorite, sodium silicate, in the centrifugal casting of iron and non ferrous metals. Further, DE-AS 1,296,750 relates to the addition of liquid borax-lime-soda-window glass-mixtures when centrifugal casting iron, wherein, these mixtures have been heated to a temperature above the temperature of the iron melt. An apparatus similar to initially mentioned kind is usual for the delivery of additives, and is known from FR-A 2,481,624 or, JP-A 56-131,157. When producing centrifugal castings of copper or copper alloys, an oxidation layer forms on the inner surface of the castings as a result of oxidation, which layer must be turned out. The thickness of this oxidation layer depends in particular, on the wall thickness of the casting and from the amount of oxygen that is absorbed during the casting process and during cooling. A disturbing oxidation layer of considerable thickness is formed even at relatively thin wall thicknesses of approximately 15 to 20 mm, and this increases in proportion to the wall thickness. In the case of thicker castings, the thickness of this layer, which has to be turned off, can amount to up 15% of the wall thickness. The thickness of this oxidation layer is, in particular, affected by the cooling speed of the melt and the length of time during which the melt on the inner surface of the casting retains higher temperature since atmospheric oxygen has an unfavourable effect and affects the thickness of the oxide layer that forms on the inside surface.